The government of Chile has extended Daylight Saving Time for 2012 [Official Decree]. DST for mainland Chile now ends on April 28, 2012 and starts on September 1, 2012.
A hotfix for Windows has been released to address this change. You can find details of the hotfix and download it here [KB2681116].
Hotfixes are available for support versions of Windows 7, Windows Server 2008 R2, Vista, Windows Server 2008, Windows XP and Windows Server 2003 platforms.
For more information on the impact of the change (including details on configuring Outlook), see the Microsoft CTS LatAm team's blog: http://blogs.technet.com/b/latam/archive/2012/02/27/chile-dst-2012-fallback.aspx.